Hello,
In explorer, properties of the hard drive say it is 20 GB. In the bios, detection say it's 300 GB. WHY?
excluding any other drive letters like A and B (floppy) or any CD/DVD drives how many do you see for regular hard drives, your 300GB drive could be partitioned into smaller drives, and you may have simply looked at the wrong one. if all else fails right click My computer (windows key + pause/break key does the same thing) select properties and goto device manager then disk drives look at the model number, write it down and google it.